The present invention relates to video display systems and, more particularly, to a novel pellicle and a method for making the pellicle for use in an improved elastomer light valve which is capable of operating at much lower voltages than have heretofore been possible.
Elastomer light valves are typically used with an optical subsystem, such as a Schleiren optical system or the like, to convert video signals into a viewable image projected on a screen. The light valve includes a deformable material, such as silicone elastomer gel or the like, disposed between a set of electrodes arrayed on a substrate and a thin conductive layer which serves as both a common electrode and a light reflective layer. A layer of material is typically disposed between the conductive layer and the elastomer gel to chemically separate them. The array of electrodes is divided into smaller groupings which collectively form a plurality of picture elements, or pixels. The pixels are typically arranged in uniform rows and columns to form an X-Y matrix structure.
In a typical video display device, electronic circuitry receives and samples a video signal; the sampled video signal is converted to control voltages which are selectively applied to the individual pixel electrodes via a combination of a plurality of X-address lines (typically one for each row ,or column, of pixels), a plurality of Y-address lines (one for each column ,or row, of pixels) and a semiconductor switch (such as a thin-film field-effect transistor or the like). The voltages applied to the pixel electrodes, relative to the thin conductive layer, create a charge pattern on the array of electrodes which causes the deformable elastomer gel and thin conductive layer to deform, or ripple, in a pattern determined by the magnitude and polarity of the applied voltages. Light incident upon the light-reflective surface of the thin conductive layer will be reflected and diffracted. The reflected light may be projected as a viewable image on a screen by a Schleiren optical system as disclosed in U.S. Pat. No. 3,084,590.
Control voltages of some conventional light valves may be as high as 100 volts or more to achieve acceptable deformation of the light reflective conductive layer. Low voltage operation is desired, however, since the individual pixels are preferably driven by amorphous silicon (a-Si) field-effect transistors (FETs) because of their potentially small size, low power consumption, favorable switching speeds, ease of fabrication, and compatibility with light valve structures. High control voltages are also undesirable because they may cause the elastomer gel layer and the light-reflective conductive layer disposed thereon to lag substantially or stick before returning to an undeformed condition after the control voltages are turned off.
Early attempts to construct a low voltage light valve were not very successful. One construction involved depositing a layer of metallization (for the reflective conductive layer) directly on the soft, tacky and spongy surface of the elastomer gel. An adverse chemical reaction occurred between the metal and the elastomer gel, causing the gel to darken and stiffen at the interface and causing a reduction in the sensitivity of the light valve to the control voltages. The gel also caused some etching of the metal layer and the highly-desirable specular character of the metal top surface was degraded.
This construction was modified to include a pellicle, formed from a plastic or nitrocellulose material, positioned as an interface between the elastomer gel and the reflective conducting electrode to isolate the two chemically-incompatible materials. This structure permitted some reduction in control voltages, although further reduction in operating voltages, to values below about 20 volts and as low as about 5 volts, are desired in some applications. The magnitude of the control voltages required for adequate deformation will be a function of the elasticity of the materials from which the pellicle and the conductive layer are made and the thicknesses of these materials.
It is accordingly a primary object of the present invention to provide a novel elastomer light valve structure which is not subject to the foregoing disadvantages.
It is a further object of the present invention to provide an elastomer light valve which is highly sensitive to low control voltages.
These and other objects of the invention, together with the features and advantages thereof, will become apparent from the following detailed specification when read with the accompanying drawings in which like reference numerals refer to like elements.